LAUSR

Abstract Regional-scale mountain pine beetle (Dendroctonus ponderosae) outbreaks in the first decade of the 2000s affected millions of hectares of lodgepole pine (Pinus contorta) in western North American forests. In Colorado, 1.4 million ha exhibited high mortality. These events prompted questions about whether historical outbreaks reached the scale of this most recent event. We aimed to reconstruct past mortality events in lodgepole pine forests in the northern Colorado Front Range and to determine whether these were of similar extent to the 2000s outbreak. We identified logs of mountain pine beetle-killed trees based on visually identifiable signs of beetle infestation including lower bole breakage, egg galleries, exit holes, and the presence of blue stain. We collected cross-sections, developed tree ring chronologies and determined death dates through tree ring analysis. We detected five mortality events since the 1860s, including widely distributed mortality in the 1910s that was geographically as extensive as the 2000s outbreak in our study area. Trees killed were on average 232 years of age and 36 cm in diameter. In our study area, it takes about 200 years for a lodgepole pine to reach the size suitable for mountain pine beetle attack. We conclude that mountain pine beetle infestation signs remain useful for identifying mountain pine beetle-caused tree mortality for over a century and that well-distributed mountain pine beetle-caused mortality has occurred in the past in the northern Colorado Front Range. Future reconstructions of bark beetle-caused mortality may benefit from integrating the use of beetle symptomatology with growth releases. The inclusion of stand demography and fire history will present a holistic picture of how disturbance interactions create the mosaic of forest landscapes. Awareness of the disturbance histories in forests and the legacies of past events advances understanding of their ecology and will inform researchers and managers in developing management strategies to foster sustainable delivery of ecosystem services and maintain resiliency as climate change manifests.